1. Field of the Invention
The present invention relates generally to a sliding element for a mechanical seal or the like. More particularly, the invention relates to a sliding element which reduces a friction coefficient on the sliding surface and prevents a process fluid from leaking from the sliding surface.
2. Description of the Related Art
Related art of the present invention is found in U.S. Pat. No. 5,080,378. The description and drawings of U.S. Pat. No. 5,080,378 discloses a mechanical seal as shown in FIG. 8. This mechanical seal 100 is located between a rotary shaft 130 and a housing 140. The mechanical seal 100 is used for sealing a fluid like water in pumps or refrigerators.
In this mechanical seal 100, a rotary seal ring 101 made of sintered porous silicon carbide is fitted over the rotary shaft 130. The rotary seal ring 101 retains a seal face 102 on its side surface. Furthermore, packings 120A, 120B are disposed in a step shoulder 103 of the inner diameter surface of the rotary seal ring 101 to seal against the rotary shaft 130.
The packings 120A, 120B are pressed by a gland ring 105 and seal the interface of the rotary shaft 130 and the rotary seal ring 101. A support ring 109 which is fixed to the rotary shaft 130 by means of a socket screw 108 supports a spring element 106, and the gland ring 105 is resiliently urged by the spring element 106.
An opposing seal face 111 which forms a slidably sealing contact with the seal face 102 is disposed in a fixed seal ring 110. The fixed seal ring 110 is secured via O-rings 115,115 to a bore of the housing 140 through which the rotary shaft 130 extends. This fixed seal ring 110 is made of carbon.
In a conventional mechanical seal 100 arranged as mentioned above, the rotary seal ring 101 and the fixed seal ring 110 slide with respect to each other while maintaining a sealing therebetween in order to seal a higher pressure side P1 from a lower pressure side P2.
The rotary seal ring 101 has a sintered silicon carbide body in which spherical pores whose average diameter is in a range of from 0.010 mm to 0.040 mm are spread within its crystalline structure, and a process fluid captured inside the pores reduces a sliding friction.
The pores located in the sliding surface of the sintered silicon carbide body are fabricated by adding polystyrene beads in a pre-sintering process and then resolving and sublimating them in a temporary sintering. This process provides a sintered silicon carbide body with pores scattered inside the crystal and penetration of the process fluid into them. From a fabrication standpoint, a difficulty in high compression molding causes a decrease in dimensional accuracy of the molded product. Also polystyrene beads resolved in the sintering process decreases the strength of a sintered material as a sliding element.
There is an enhanced version of mechanical seal which improves the aforementioned problems in terms of the strength decrease of the sliding element and the process fluid leakage.
This mechanical seal has the same constitution as what is shown in FIG. 8. FIG. 9 shows a rotary seal ring 205 disposed in the mechanical seal. The sliding faces of the rotary seal ring 205 fixed to a rotary shaft and a fixed seal ring retained in the housing form a sealing contact to seal a process fluid.
The sliding face of the rotary seal ring 205 retains a lot of concaves 206. Minimum width of the concave 206 is in a range of from 30×10−6 m to 100×10−6 m while the maximum width is in a range of from 60×10−6 m to 500×100−6 m, and the maximum width is more than twice in dimension of the minimum width.
The grooves 206 prevent the process fluid entering from the outer circumference side between the sliding face 205A of the rotary seal ring 205 and the seal face of the fixed seal ring from bleeding to the inner circumference.
The sealing situation is further explained in details. The process fluid entering from the outer circumference side of the rotary seal ring 205 is trapped and stored in the concave 206 on its way to the inner circumference side. The fluid stored in the concave 206 is pushed back from the outer circumferential edge to the fluid side as the result of the radially outward movement of the fluid relative to the concave 206 due to viscosity of the fluid and rotary motion of the rotary seal ring 205. However, this kind of concave 206 is nothing but a segmented arrangement of a conventional spiral groove as shown in FIG. 9, and its pumping effect to push back the process fluid is small. Also a decrease in the friction coefficient of the sliding face for reducing the heat generation due to friction cannot be expected.
Also there has been other prior art sliding element for mechanical seals. The sliding face of the sliding element for mechanical seals disposes plural dimples lined up like a groove along a longitudinal direction which is vertical to a sliding direction. Dynamic pressure generated within the dimples is fairly large. Thus, a lubricant oil film of the fluid is formed thick and a pushing back force to the process fluid side becomes small, hence a decrease in a seal performance.
The present invention is introduced to resolve the above mentioned problems. A primary technical goal which this invention tries to achieve is to form a film of process fluid on a sliding face by utilizing a sliding effect for reducing a frictional resistance and effectively retaining the incoming fluid on the sliding face.
Another goal is to prevent friction and heat generation on the sliding face which may cause a squeaking noise or a torque variation on the sliding face, which will lead to a wear of the face due to fluctuations.
Yet another goal is to push back a process fluid penetrating into the sliding face gap by means of dimples and to prevent the fluid residing on the sliding face from bleeding to an atmospheric side.
Yet another goal is to preserve strength of the sliding face of the sliding element, to prevent damage of the sliding face, and to enhance the durability.